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Quantifying systolic and diastolic cardiac performance from dynamic impedance waveformsRelated Patent Categories: Surgery: Light, Thermal, And Electrical Application, Light, Thermal, And Electrical Application, Electrical Therapeutic Systems, Heart Rate Regulating (e.g., Pacing), Parameter Control In Response To Sensed Physiological Load On HeartQuantifying systolic and diastolic cardiac performance from dynamic impedance waveforms description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070191901, Quantifying systolic and diastolic cardiac performance from dynamic impedance waveforms. Brief Patent Description - Full Patent Description - Patent Application Claims
PRIORITY CLAIM [0001] This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 11/335,377, filed Jan. 18, 2006, which is a continuation of U.S. patent application Ser. No. 10/860,990, filed Jun. 4, 2004, now U.S. Pat. No. 7,010,347, all of which are herein incorporated by reference in their entirety. FIELD OF THE INVENTION [0002] This invention pertains to an implantable CRT device that includes electrodes and means for dynamically measuring various impedance-related parameters and using these parameters for programming the CRT. BACKGROUND [0003] Current implantable cardiac resynchronization devices (CRT) are designed to improve congestive heart failure systems in cardiomyopathy patients with electromechanical dysynchrony. Most physicians implant CRTs without modification of the default programmed interval timing and as such a significant percentage of patients do not have improvements in heart failure symptoms. Current CRT essentially pace the RV and LV simultaneously. However, future CRTs will have a programmable delay between pacing in the RV and LV. [0004] A CRT device that optimizes timing intervals based on impedance measurements is described in U.S. Patent Pub. No. 2003/0204212 to Burnes et al., herein incorporated by reference in its entirety. Burnes describes the use impedance-based measurements based upon identification impedance maxima and minima. Burnes discloses that changes in atrial-ventricular interval timing are performed as to "converge on the AV interval causing maximum impedance change indicative of maximum ventricular output." (see Burnes Abstract). Additionally, Burnes describes "another method varies the right ventricle to left ventricle interval to converge on an impedance maximum indicative of minimum cardiac volume at end systole". Id. "Another embodiment varies the VV interval to maximize impedance change." Id. SUMMARY [0005] A substantial amount of data is available that demonstrates that small changes in interval timing between the RV and LV can reduce dysynchrony and improve congestive heart failure symptoms. As the status of an individuals heart can change acutely (congestive heart failure, myocardial ischemia/infarction) or chronically (remodeling) changes in interval timing may be needed over time. Ideally, CRTs can self adjust this interval timing as part of a closed loop system. Parameters based on extrinsic diagnostic evaluations such as ultrasound imaging or measurements of extra-thoracic impedance to guide programming of CRT may be useful at periodic intervals but implementing such modalities can be time consuming. Use of an interface between CRT and extrinsic diagnostic systems will help accomplish CRT programming, but will not provide a dynamic means of control. Intracardiac electrograms and impedance measurements provide a window into intrinsic electromechanical events and are ideal for use in such a control system. Signal processing of impedance data over time has limitations. The methods and means of identifying which impedance signals are adequate for use as diagnostic data for monitoring purposes is described herein. Such diagnostic data is then optimized and implemented as to direct programming of interval timing in a closed loop control system. [0006] Some embodiments relates generally to implantable cardiac devices such as pacemakers and defibrillators that deliver cardiac resynchronization therapy (CRT), and to a method of optimizing acquisition of multi-vector impedance signals from electrodes present on implanted lead systems. In some embodiments, acquired impedance signals associated with dynamic intracardiac impedance are related to specific time frames of the cardiac cycle as to derive indices representative of systolic and diastolic cardiac performance. The impedance signals are further adjusted by non-dynamic or static impedance signals associated with pulmonary impedance as to derive composite indices representative of cardiac performance and pulmonary vascular congestion. The pulmonary impedance signals are preferably obtained during relative periods of apnea in a patient. [0007] In one embodiment, a method of controlling a cardiac resynchronization therapy (CRT) device is provided, comprising measuring a dynamic intrathoracic impedance from three or more electrode sites, wherein at least one electrode site is a non-intracardiac electrode site; determining a control parameter associated with the dynamic intracardiac impedance data of a patient; measuring a pulmonary impedance using the non-intracardiac electrode site and another of said three or more electrode sites; reducing the control parameter based upon the thoracic impedance; and setting an operational parameter of said CRT device based on a difference between said control parameter and a reference value. Measuring the impedances may comprise measuring the impedances from multiple vectors between the three or more electrode sites. The non-intracardiac electrode site may be selected from a group consisting essentially of a device can of the CRT device, a pericardial lead, a left ventricle lateral coronary sinus lead, and a superior vena cava coil. The method may further comprise acquiring dynamic impedance data associated with both a systolic phase and a diastolic phase of the patient. The dynamic impedance data associated with the diastolic phase of the patient may have an inverse relationship with the control parameter. The method may further comprise delivering an electrical stimulus during an absolute refractory phase of the patient based upon the operational parameter. The method may further comprise acquiring the dynamic intracardiac impedance data using a variable sampling rate. Determining the control parameter may be performed within said CRT device. Reducing the control parameter may be performed within said CRT device. Measuring the dynamic intrathoracic impedance may be performed over two or more cardiac cycles. The two or more cardiac cycles may be consecutive cardiac cycles. The method may further comprise correlating the dynamic intrathoracic impedance with a concurrent respiratory cycle. The method may further comprise selecting a subset of the dynamic intrathoracic impedance correlating to a specific respiratory phase of the respiratory cycle. The specific respiratory phase may be the end-expiratory phase or the end-inspiratory phase. The method may further comprise associating the dynamic intrathoracic impedance with a respiratory rate; and selecting a subset of the dynamic intrathoracic impedance within a range of respiratory rates. The reference value may be a prior control parameter determined at rest. [0008] In another embodiment, a method of controlling a cardiac resynchronization therapy device is provided, comprising measuring a first intrathoracic impedance between a first pair of electrode sites, wherein the first pair of electrode sites are intracardiac electrode sites; measuring a second intrathoracic impedance between a second pair of electrode sites that is different from the first pair of electrode sites; determining a control parameter associated with the first intrathoracic impedance data and the second intrathoracic impedance data, wherein the first intrathoracic impedance data and the second intrathoracic impedance data have opposing effects with respect to the control parameter; and setting an operational parameter of said CRT device based said control parameter. One electrode site of the second pair of electrode sites may be selected from a group consisting essentially of a device can of the CRT device, a pericardial lead, a left ventricle lateral coronary sinus lead, and a superior vena cava coil. The second pair of electrode sites may be intracardiac electrode sites. [0009] In another embodiment, a cardiac resynchronization therapy system is provided, comprising a CRT device configured to apply therapy to a patient based on a plurality of operational parameters; detect a dynamic intrathoracic impedance of the patient, wherein the dynamic intrathoracic impedance comprises a dynamic intracardiac impedance component and a pulmonary impedance component; calculate a control parameter from the dynamic intracardiac impedance component and a pulmonary impedance component; evaluate if said control parameter is acceptable; and set said operational parameters based on said control parameter, if said control parameter is found acceptable. The control parameter may have a negative relationship with the pulmonary impedance component or the dynamic pulmonary impedance component. The dynamic intrathoracic impedance of the patient may further comprise a dynamic pulmonary impedance component. [0010] In another embodiment, an implantable CRT system is provided, comprising a sensor system that senses intrinsic cardiac events and generates corresponding sensing signals; and an implantable CRT device configured to accept sensing signals from the sensor system, generate excitation signals for different locations of a heart in response to commands, generate said commands in accordance with a plurality of operational parameters dependent on said sensing signals, generate a control parameter dependent on a thoracic impedance of a patient, wherein the thoracic impedance comprises an intracardiac impedance component and a pulmonary impedance component; and determine if said control parameter is acceptable based on a set of preset criteria, wherein said implantable CRT device is configured to be to increase cardiac performance by increasing cardiac output. The control parameter may be configured to have a negative relationship with the pulmonary impedance component. The control parameter has a positive relationship with the pulmonary impedance component. BRIEF DESCRIPTION OF THE DRAWINGS [0011] FIG. 1 and FIG. 2 depict the apparatus and flow diagram for automatically programming a CRT device. [0012] FIG. 3, FIG. 3a and FIG. 3b depict the rotation and translation of the left ventricle (LV) during the cardiac cycle using ultrasound techniques of Tissue Velocity Imaging. FIG. 3a illustrates how the regions sampled are relatively orthogonal to ultrasound beam. FIG. 3b illustrates the septal and lateral wall regions of interest. [0013] FIG. 4 illustrates the effects of extracardiac structures on impedance measurements. [0014] FIG. 5 shows varying degrees of impedance signal fidelity requirements. [0015] FIG. 6 demonstrates valvular event timing during the cardiac cycle and the relationship between the impedance signal and Doppler derived measurements of blood flow across the aortic valve as to accurately denote time of aortic valve closure. [0016] FIG. 7 illustrates cardiac chamber anatomy suitable for lead placement of electrodes that provide trans-valvular (aortic valve) impedance data. [0017] FIG. 8 depicts the relationship of impedance waveforms derived from right ventricular (RV and LV vectors to myocardial strain (or velocity curves) representative of time to peak impedance and time of peak myocardial strain (or velocity), respectively. [0018] FIG. 9 shows changes in impedance waveforms with myocardial ischemia. [0019] FIG. 10 shows impedance waveforms derived from RV trans-valvular electrodes and LV electrodes which have been summated to derive a more global representation of cardiac performance and dysynchrony. Continue reading about Quantifying systolic and diastolic cardiac performance from dynamic impedance waveforms... 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